Harvest Moon

The beautiful full Moon decorates the sky tonight. It's low in the east as night falls, shining orange or gold through the fading twilight, and sails high across the sky during the night. And it's not just any old Moon -- it's the most famous full Moon of all: the Harvest Moon.

The Harvest Moon is generally defined as the full Moon closest to the autumnal equinox -- the beginning of autumn here in the northern hemisphere. And this year, the Moon pretty much nails it. The equinox occurs at 10:09 p.m. Central Daylight Time, with the Moon reaching "full" a bit more than six hours later.

As you might expect, this is a rare coincidence. The Moon's cycle of phases lasts a bit less than 30 days, so it doesn't line up with the calendar. That means the dates of the full Moons move around from year to year. So in any given year, the odds of the full Moon occurring this close to the equinox are about 1 in 60.

But that's an average, so it doesn't mean the alignment is this close only every 60 years or so. In fact, it last happened in 1972, and it'll happen again in 2029.

This year, the Harvest Moon is especially beautiful because it has a bright companion: the planet Jupiter, which outshines everything else in the night sky except the planet Venus and the Moon itself. Jupiter rises a little below the Moon, and they remain close throughout the night.

More about Jupiter and the Moon tomorrow.

Script by Damond Benningfield, Copyright 2010

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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